Secondary battery having third terminal other than positive and negative electrode terminals and battery comprising it

ABSTRACT

A secondary battery in which temperature rise (heat generation) can be measured accurately at the time of quick charge/discharge, and a battery which can be configured readily using the secondary batteries while realizing low resistance. Separately from the positive and negative electrode terminals of a flat laminate film secondary battery, a third terminal is fixed perpendicularly thereto. The third terminal is connected with the electrode current collecting parts of a power generating element body constituting the secondary battery ( 1 ) and imparted with a potential equal to that of any one of the positive and negative electrode terminals. Inner temperature of the secondary battery is determined by measuring the temperature of the third terminal and a cell balancer circuit, or the like, is connected with the third terminal. The battery is configured by connecting the positive and negative electrode terminals directly in series.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a secondary battery and a storagebattery made up of the secondary batteries.

BACKGROUND OF THE INVENTION

Recently, there has been growing a demand for a battery of a largestorage capacity using secondary batteries. Specifically, the demand hasbeen growing in the applications of electric bicycles, electric bikesand electric motorcars, the attention having been focused on batteriesof a 100 W to 1000 W. class and also the batteries having an outputhigher than 1000 W.

The conventional large storage-capacity batteries using secondarybatteries have been made up of several lead cells or nickel hydrogencells in combination, and those having large sizes, low weight andvolume densities and also of high costs have been prevalent. For thisreason, realizing a large storage-capacity battery having a small sizeand high weight and volume densities and also of a low cost has beendesired.

A high-voltage lithium ion secondary battery, which serves as anelemental cell of a storage battery, has recently been realized, inwhich a lightweight laminate film is used as a casing. It is expectedthat the development of a storage battery with use of this lithium ionsecondary battery will make it possible to realize a battery of a lowcost and a large storage capacity having a small size and high weightand volume densities.

However, even if a storage battery of such a low cost and a largestorage capacity having a small size and high weight and volumedensities can be realized, many problems are still left to be solved. Inparticular, when the battery is used for an automobile car, rapidcharge/discharge characteristics as well as a high cycle life arerequired, which gives rise to many problems promptly to be solved suchas the lowering of an internal resistance of the battery; aheat-generation problem due to rapid charging; problems in the controlof the cell balance in the interior of the battery; and the realizationof a highly precise cycle-life predicting circuit.

In order-to solve these problems, it is absolutely necessary toprecisely measure the temperature in the interior of the cell. In theconventional secondary battery, it has been common to perform themeasurement of the internal temperature by setting a temperature sensoreither on a surface layer of the secondary battery or on thepositive/negative electrode terminal.

Mounting a temperature sensor on a surface layer of the secondarybattery, however, makes it difficult to stack a plurality of secondarybatteries when building up a storage battery, because the stackarrangement of flat secondary batteries each with a casing of laminatefilm has temperature sensors interposed between the secondary batteries,which could result in detecting average temperatures between the stackedsecondary batteries, or cause any damage to the secondary batteryitself. In some cases, an arrangement has been adopted in which elasticmaterial such as sponge sheets are sandwiched between the secondarybatteries, in order to stack secondary batteries avoiding contact withthe temperature sensors. The arrangement, however, entails not onlylowering of the weight and volume densities but also an increase in thenumber of processes of constructing the storage battery as well as anincrease in component costs.

Attaching a temperature sensor to an electrode terminal, on the otherhand, requires an extra long terminal. Consequently, the construction ofthe storage battery requires a larger volume to accommodate the extralength of terminal, entailing the lowering of the volume density.Furthermore, the heat generated in the electrode terminal by the rapidcharge/discharge operation causes the temperature sensor to detect thetemperature of the electrode terminal rather than the temperature in theinterior of the secondary battery. This has been responsible for theoccurrence of the deviations in the life prediction of the secondarybattery.

Furthermore, it has been common practice in connecting a cell-balancercircuit or the like to a storage battery to draw out the lead wires forthe cell-balancer circuit from charge/discharge electrode terminals ofcells when the cells are connected to one another, or to perform theconnection between cells through a bus-bar and then draw out the leadwires for the cell-balancer circuit from the bus-bar. As a result, notonly the installation of a control system such as a cell-balancer hasbeen troublesome but also the drawing out lead wires for a cell-balancercircuit from the charge/discharge electrode terminals has prevented theelectrode terminals from being shortened, entailing difficulty inlowering the internal resistance of the storage battery.

SUMMARY OF THE INVENTION

It is an object of the present invention to achieve reduction of theinternal resistance of a battery as well as to improve the accuracy inthe measurement of the temperature rise (or heat generation) in asecondary battery caused by a rapid charge/discharge operation of thebattery. It is another object of the present invention to provide asecondary battery that allows easy construction of a storage battery andalso to provide a storage battery through the use of the secondarybatteries.

In order to accomplish the objects, the secondary battery of the presentinvention is provided with a third terminal formed to extend from eitherone of the positive and negative electrode collectors in anelectric-power generating element included in the secondary battery, inaddition to the positive and negative electrode terminals for charge anddischarge. The third terminal has the same potential as the potential ofthe either one of positive and negative electrodes. In this way, itbecomes feasible to achieve above-described objects withoutnecessitating significantly modifying the shape of the conventionalsecondary battery and by adding only one step to the fabrication processof a secondary battery.

Attaching a temperature sensor to the third terminal isolates thetemperature sensor from the influence of heat generation in the positiveand negative electrode terminals for charge and discharge, therebyenabling accurate detection of the internal temperature of the secondarybattery, i.e., the temperature of the electric-power generating element.

Furthermore, extending the third terminal in the direction perpendicularto the extension direction of the positive and negative electrodeterminals facilitates the installation of the cell balancer circuit inconstructing the battery. The reason for this is that, since the thirdterminal has the same potential as either one of the positive andnegative electrodes, the third terminal can be used for the connectionwith a control system such as a cell balancer, while performinginter-cell connection through individual direct connections of thepositive electrode terminals and the negative electrode terminals of thesecondary batteries, when the storage battery is built up.

The present invention enables an accurate measurement of an internaltemperature of a flat laminate-film secondary battery, thereby allowingprecise prediction of a cycle life of the battery, by forming, inaddition to the positive and negative electrode terminals for charge anddischarge, a third terminal, which has the same electric potential aseither one of the positive and negative electrode terminals, to extendfrom the electric-power generating element and by measuring thetemperature of the third terminal, as described above. Furthermore, itbecomes feasible to have the secondary batteries laminated more compactin building up a storage battery.

Since the third terminal assumes an electric potential and is alsousable as a section to attach a lead wire for a cell balancer circuit aswell, the wiring for control can easily be routed in building-up astorage battery, resulting in facilitating the installation of a controlsystem such as a cell balancer and the like. As a result, it is enabledto simplify the fabricating process of a battery, further reducing aproduction cost.

Furthermore, since it becomes unnecessary to attach temperature sensorsand lead wires for a cell balancer circuit to the positive/negativeelectrode terminals, the electrode terminals can be shortened to optimumlengths, and also can more easily be connected directly to each other,whereby the internal resistance of the storage battery is reduced.

BRIEF EXPLANATION OF THE DRAWINGS

FIG. 1 is a perspective view of a flat laminate-film secondary batteryaccording to an embodiment of the present invention.

FIG. 2 is a perspective view of a conventional flat laminate-filmsecondary battery.

FIG. 3 is a diagram illustrating an internal structure of anelectric-power generating element.

FIG. 4 is a perspective view of a flat secondary battery.

FIG. 5 is a diagram illustrating a structure of a flat laminate-filmsecondary battery.

FIG. 6 is a perspective view of a flat secondary battery of analternative embodiment.

FIG. 7 is a diagram illustrating a structure of a storage battery usingflat laminate-film secondary batteries according to an embodiment of thepresent invention.

FIG. 8 is a diagram illustrating an example of building up a storagebattery using flat laminate-film secondary batteries.

FIG. 9 is a diagram illustrating a structure of a storage battery usingconventional flat laminate-film secondary batteries.

PREFERRED EMBODIMENTS OF THE PRESENT INVENTION

Referring to FIG. 1, flat laminate-film secondary battery of anembodiment of the present invention 1 has third terminal 4 in additionto positive electrode terminal 2 and negative electrode terminal 3. FIG.2 illustrates a conventional flat laminate-film secondary battery.

Flat laminate-film secondary battery 1 of the present embodiment isconstructed as described below.

First, anode elements 5 and cathode elements 6 are alternately stackedwith separators 7 interposed between them, thereby forming anelectric-power generating element 8 as shown in FIG. 3.

Next, positive electrode terminal 2 and negative electrode terminal 3are attached to uncoated sections (electrode collectors) 2 a and 3 a,free of active material, of anode elements 5 and cathode elements 6,respectively, as shown in FIG. 4.

Next, third terminal 4 is directly connected to either one of uncoatedsections 2 a and 3 a of anode elements 5 and cathode elements 6,respectively, of electric-power generating element 8, as shown in FIG.4. In FIG. 4, third terminal 4 is connected to uncoated sections 2 a ofanode elements 5 in electric-power generating element 8, wherein thirdterminal 4 is attached in such a way that it does not contact positiveelectrode terminal 2. It is desirable to separate both of the terminalsas far as possible from each other in order to minimize the influence onthird terminal 4 of the heat generation possibly generated in positiveelectrode terminal 2 by rapid charge.

Next, as shown in FIG. 5, electric-power generating element 8, in whichpositive and negative electrode terminals 2 and 3 and third terminal 4are incorporated, is wrapped with laminate-film casing 9, which issealed on the three sides by means of hot-melt fusion-bonding, andthereafter, non-aqueous electrolyte is injected into the laminate-filmcasing 9, which is then completely sealed under a reduced pressure, asin the conventional process of fabricating a laminate-film secondarybattery.

Uncoated sections (electrode collectors) 2 a, 3 a, which are free ofactive material, of anode elements 5 and cathode elements 6,respectively, in electric-power generating element 8 may be arranged inopposed positions, as shown in FIG. 6.

Detailed explanation will next be presented regarding an example of aflat laminate-film secondary battery 1 of the present embodiment.

In a first example of the present invention, anode elements 5 andcathode elements 6 are alternately stacked with separators interposedbetween the anode and cathode elements and also with their electrodecollectors (uncoated sections) 2 a and 2 b extended outwards from thesame side, wherein each of the anode elements 5 comprises a sheet ofaluminum foil of 20 μm in thickness to which is applied, on both faces,lithium-ion containing metal oxide natured to occlude/release a lithiumion, such as lithium-manganese composite oxide, approximately 70 μmthick; each of cathode elements 6 comprises a sheet of copper foil 15 μmthick to which is applied, on both faces, approximately 50 μm-thickhard-carbon based cathode active material that occludes/releases alithium ion; and separator 7 is a laminate separator of a polypropylenefilm and a polyethylene film, which are sheets of porous insulator resinfoils 25 μm thick each. A 100 μm-thick aluminum positive electrodeterminal 2 and a 100 μm-thick nickel negative electrode terminal 3 areattached to electrode collectors (uncoated sections) 2 a and 3 a,respectively, of anode elements 5 and cathode elements 6 by means ofultrasonic welding.

An aluminum terminal of 100 μm in thickness is next attached to positiveelectrode collector (uncoated sections) 2 a by means of ultrasonicwelding so as to extend outwards from the collector 2 a in the directionperpendicular to the direction of the extension of the positive/negativeelectrode terminal, to provide third terminal 4. While the ultrasonicwelding is employed in the first example, any method capable ofproviding electrical conductivity, such as the resistance welding orriveting, may be employed.

Electric-power generating element 8 constructed in this way is nextwrapped with an about 100 μm-thick laminate film of aluminum foil 9,into which is injected the electrolyte produced by dissolving lithiumphosphate hexafluoride with non-aqueous solvent of propylene carbonateand methyl ethyl carbonate; and the laminate film is then sealed bymeans of hot-melt fusion-bonding under a reduced pressure.

The size of anode element 5 is 65 mm×120 mm, the size of cathode element6 being 70 mm×125 mm, the size of separator 7 being 75 mm×130 mm, thesizes of positive and negative electrodes 2, 3 being 40 mm×10 mm, thesize of the third terminal being 30 mm×5 mm, the size of laminate film 9for the casing being 95 mm×160 mm and the width of the hot-meltfusion-bonding seal being 10 mm.

In a second example, third terminal 4 of nickel is formed extending fromnegative electrode collector 3 a.

In a third example, anode elements 5 and cathode elements 6 arealternately stacked sandwiching separator 7 therebetween so thatelectrode collector 2 a and electrode collectors 3 a (both being theuncoated sections) will be arranged opposite each other, and thirdterminal 4 of aluminum is formed extending from an end of electrodecollector 2 a of anode elements, perpendicularly to the direction inwhich positive and negative electrodes extend and further in theposition sufficiently remote from positive electrode terminal 2, asshown in FIG. 6.

In a fourth example, third terminal 4 of nickel is formed extending froman end of electrode collector (uncoated sections) 3 a of cathodeelements of electric-power generating element 8 perpendicularly to thedirection in which positive and negative electrodes extend and furtherin the position sufficiently remote from negative electrode terminal 3,wherein electric-power generating element 8 of the fourth example is thesame as that of the third example.

The constituent elements and the dimension of the constituent elementsemployed in the second to fourth examples are identical to thoseemployed in the first example. These examples differ from one anotheronly in that the directions in which the positive and negativeelectrodes extend differ and that the potential applied to thirdterminal 4 differs. The flat laminate-film secondary batteries 1disclosed in the first to fourth examples have 4.2 V (2 Ah)characteristics. The thickness is 4 mm, and the weight is 80 g.

Table 1 represents the result of the measurements of the temperature inthe interior of a flat laminate-film secondary battery 1 disclosed ineach of the first to fourth examples. The measurements were carried outas follows. The forced discharge of 50 A for 5 sec. was performed at anambient temperature of 20° C., and then maximum attained temperatureswere measured by means of thermocouples at positive and negativeelectrode terminals 2, 3, third terminal 4 and three places on thesurface of the flat laminate-film secondary battery. Temperature rises(differences) with respect to the surface temperatures were determinedat each site. Table 1 represents the temperature rises.

It is presumed that the surface of the flat laminate-film secondarybattery 1 is in the thermal equilibrium with the interior of thebattery, the surface temperature representing an approximate internaltemperature. In the prior art, it has been common practice to regard thetemperature of positive/negative electrode 2, 3 as an internaltemperature of the flat laminate-film secondary battery.

TABLE 1 1st 2nd 3rd 4th example example example example Temperaturedifference 30.5 29.5 30.0 30.5 (° C.) of positive electrode terminalTemperature difference 49.5 48.5 49.5 48.5 (° C.) of negative electrodeterminal Temperature difference 3.5 — 0 — (° C.) of third terminal (onthe positive electrode collector) Temperature difference — 9.0 — 1.0 (°C.) of third terminal (on the negative electrode collector)

As is seen from Table 1, the temperature differences of the positive andnegative electrode terminals (the differences from the surfacetemperature of the cell) in the first and second examples aresignificantly large, approximately 30° C. at the positive electrodeterminal and a little under 50° C. at the negative electrode terminal.The temperature differences in the third terminal, in contrast, are 3.5°C. on the positive electrode collector and 9.0° C. on the negativeelectrode collector, indicating that the temperature in the thirdterminal approximates the internal temperature of the cell with muchhigher accuracy than the method of measurement according to prior art.In the third and fourth examples as well, the temperature differences ofthe positive and negative terminals (the differences from the surfacetemperature of the cell) are large, indicating approximately 30° C. atthe positive electrode terminal and a little under 50° C. at thenegative electrode terminal.

The temperature differences of the third terminal, in contrast, are 0°C. on the positive electrode collector and 1.0° C. on the negativeelectrode collector, indicating that the third terminal exhibits thetemperature nearer the internal temperature of the cell than thetemperatures of the third terminals in the first and second examples.The reason for this is considered that the third terminals of the thirdand fourth examples are attached to the positions sufficiently remotefrom the positive and negative electrode terminals in order to be moreinsusceptible to the effect of heat generation in the positive andnegative electrode terminals than the cases of the first and secondexamples.

The flat laminate-film secondary battery 1 provided with the thirdterminal of the present embodiment allows measurement of the internaltemperature of a cell with a markedly higher accuracy than theconventional one, in any of the first to fourth examples. In addition,since the temperature difference of the third terminal tends to exhibita lower value on the positive electrode collector than on the negativeelectrode collector, it is realized that the third terminal of the thirdexample provides the nearest temperature value to the internaltemperature of a cell.

FIG. 7 illustrates an embodiment of the storage battery according to thepresent invention, which uses flat laminate-film secondary batteries 1of the present embodiment. The storage battery is structured such thatten flat laminate-film secondary batteries 1 are stacked with thepositive and negative electrode terminals for charge/discharge beingserially connected directly and further third terminals 4 being directedin the same direction. This structure is built up by stacking flatlaminate-film secondary batteries 1 of the fourth example with thepositive electrode terminals and the negative electrode terminalsindividually connected directly to make serial connections afterconnecting temperature-detecting sensors 10 and lead wires 11 for a cellbalancer circuit to third terminals 4 of the flat laminate-filmsecondary batteries 1. The flat laminate-film secondary batteries 1 arestacked to realize the highest volumetric efficiency without providingany temperature-detecting sensor, an elastic element such as a spongesheet, or the like between successive secondary batteries.

FIG. 8 illustrates a storage battery constructed by connectingtemperature-detecting sensor 10 and the lead wires 11 for a cellbalancer, which extend from the third terminals of flat laminate-filmsecondary batteries 1 built up as described above, to control circuit 12and wrapping the built-up flat laminate-film secondary batteries 1 withaluminum casing 13 of 2 mm in thickness.

Referring to FIG. 9, there is illustrated a conventional storage batteryfor comparison. The storage battery was built up through the use ofsecondary batteries each of which had basically the same structure asthe flat laminate-film secondary battery of the fourth example exceptthat it was lacking the third terminal. The conventional storage batterywas built up through the processes of attaching temperature-detectingsensor 10 to the central region of the surface of each secondarybattery; connecting each lead wire 11 for a cell balancer circuit to thepositive-electrode-terminal side of the positive and negative electrodeterminals for charge and discharge; directly connecting the positiveelectrode terminals and the negative electrode terminals individually toform serial connections; and stacking the secondary batteriessandwiching elastic sponge boards (15 g in weight, 2 mm×70 mm×120 mm insize) between successive secondary batteries. After stacking thesecondary batteries in this way, each of temperature-detecting sensors10 and each of lead wires 11 for a cell balancer circuit were connectedto control circuit 12, and the whole battery system was wrapped withaluminum casing 13 of 2 mm in thickness like the example shown in FIG.8. A conventional storage battery was produced in this way.

As a result, the storage battery of the present embodiment exhibits 35%reduction in a volume ratio and 10% reduction in a weight ratio,enabling an improvement in the weight and volume densities of thestorage battery.

In the present embodiment, the third terminals are formed extending fromthe sides of the rectangular flat laminate-film secondary batteries 1,on which none of the positive and negative electrodes for charge anddischarge are attached, in the direction perpendicular to the directionin which the positive and negative electrodes extend. The angle includedbetween the extending directions of the third terminals and the positiveand negative electrodes for charge and discharge need not necessarily beperpendicular, provided that it is feasible to install the cell balancercircuit and the like to be connected to the third terminals in a compactmanner without necessitating a superfluous space.

Furthermore, the flat laminate-film secondary battery can have a shapeother than a rectangle, provided that the shape allows the cell balancercircuit and the like to be connected in a compact manner withoutnecessitating a superfluous space.

1. A flat secondary battery comprising: an electric-power generatingelement provided with positive and negative electrode collectors, eachof said collectors having a respective uncoated area that is free ofactive material; positive and negative electrode terminals for chargeand discharge and that are attached to said uncoated areas of saidpositive and negative electrode collectors, respectively; and a thirdterminal that is attached directly to said uncoated area of one of saidpositive and negative electrode collectors and that does not directlycontact either of said positive and negative electrode terminals,wherein said third terminal and a respective one of said positive andnegative electrode terminals are attached to said uncoated area of saidone of said positive and negative electrode collectors at differentpositions in order to avoid an influence on said third terminal of heatfrom the respective one of said positive and negative electrodeterminals, wherein said third terminal has a same electric potential assaid respective one of said positive and negative electrode terminalsand said third terminal is attached electrically conductively to saiduncoated area of said one of said positive and negative electrodecollectors, and wherein a temperature of said flat secondary battery canbe measured by said third terminal.
 2. A flat secondary batteryaccording to claim 1, wherein said third terminal is formed to extend inthe direction differing from the extending direction of said positiveand negative electrode terminals for charge and discharge.
 3. A flatsecondary battery according to claim 2, wherein the direction in whichsaid third terminal extends is perpendicular to said extending directionof said positive and negative electrode terminals for charge anddischarge.
 4. A flat secondary battery according to claim 1, whereinelectric-power generating element is made up of anode elements andcathode elements alternately stacked with a separator sandwiched betweeneach anode element and each cathode element.
 5. A flat secondary batteryaccording to claim 1, provided with a casing of a laminate film.
 6. Astorage battery of a serial type using a plurality of flat secondarybatteries according to claim
 1. 7. A flat secondary battery according toclaim 2, wherein said electric-power generating element is made up ofanode elements and cathode elements alternately stacked with a separatorsandwiched between each anode element and each cathode element.
 8. Aflat secondary battery according to claim 3, wherein said electric-powergenerating element is made up of anode elements and cathode elementsalternately stacked with a separator sandwiched between each anodeelement and each cathode element.
 9. A flat secondary battery accordingto claim 1, wherein said third terminal is attached directly to saiduncoated area of said one of said positive and negative electrodecollectors at a position that is opposite and remote from a positionwhere the respective one of said positive and negative electrodeterminals for charge and discharge is attached to said uncoated area ofsaid one of said positive and negative electrode collectors.
 10. A flatsecondary battery according to claim 5, wherein said third terminal isattached to said one of said positive and negative electrode collectorsinside said casing.
 11. A flat secondary battery according to claim 1,further comprising an outer member that forms a body of the battery andwherein said third terminal is attached to said one of said positive andnegative electrode collectors inside said outer member.
 12. A flatsecondary battery according to claim 1, comprising two of said thirdterminal that are each attached to a respective one of said positive andnegative electrode collectors.